//
// Created by lenovo on 2024/6/28.
//

#pragma  once
#include <vector>
#include <queue>
#include <memory>
#include <thread>
#include <mutex>
#include <condition_variable>
#include <future>
#include <functional>
#include <stdexcept>

namespace ZYUtils {
    class ZYThreadPool {
    public:
        ZYThreadPool(size_t);

        template<class F, class... Args>
        auto enqueue(F &&f, Args &&... args)
        -> std::future<typename std::result_of<F(Args...)>::type>;

        ~ZYThreadPool();

        void clear();

        void waitUntilCompleted();

    private:
        // need to keep track of threads so we can join them
        std::vector<std::thread> workers;
        // the task queue
        std::queue<std::function<void()> > tasks;

        // synchronization
        std::mutex queue_mutex;
        std::condition_variable condition;
        bool stop;
    };

// the constructor just launches some amount of workers
    inline ZYThreadPool::ZYThreadPool(size_t threads)
            : stop(false) {
        for (size_t i = 0; i < threads; ++i)
            workers.emplace_back(
                    [this] {
                        for (;;) {
                            std::function<void()> task;

                            {
                                std::unique_lock<std::mutex> lock(this->queue_mutex);
                                this->condition.wait(lock,
                                                     [this] {
                                                         return this->stop || !this->tasks.empty();
                                                     });
                                if (this->stop && this->tasks.empty())
                                    return;
                                task = std::move(this->tasks.front());
                                this->tasks.pop();
                            }

                            task();
                        }
                    }
            );
    }

// add new work item to the pool
    template<class F, class... Args>
    auto ZYThreadPool::enqueue(F &&f, Args &&... args)
    -> std::future<typename std::result_of<F(Args...)>::type> {
        using return_type = typename std::result_of<F(Args...)>::type;

        auto task = std::make_shared<std::packaged_task<return_type()> >(
                std::bind(std::forward<F>(f), std::forward<Args>(args)...)
        );

        std::future<return_type> res = task->get_future();
        {
            std::unique_lock<std::mutex> lock(queue_mutex);

            // don't allow enqueueing after stopping the pool
            if (stop)
                throw std::runtime_error("enqueue on stopped ThreadPool");

            tasks.emplace([task]() { (*task)(); });
        }
        condition.notify_one();
        return res;
    }

// the destructor joins all threads
    inline ZYThreadPool::~ZYThreadPool() {
        {
            std::unique_lock<std::mutex> lock(queue_mutex);
            stop = true;
        }
        condition.notify_all();
        for (std::thread &worker: workers)
            worker.join();
    }

    inline void ZYThreadPool::clear() {
        std::unique_lock<std::mutex> lock(this->queue_mutex);
#ifndef NDEBUG
        //VS_LOG("task size:(%d)",this->tasks.size());
#endif

        while (!this->tasks.empty()) {
            this->tasks.pop();
            if (this->tasks.size() == 1) {
                break;
            }
        }
    }

    inline void ZYThreadPool::waitUntilCompleted() {
        std::unique_lock<std::mutex> lock(this->queue_mutex);
        condition.wait(lock);
    }
}